The present invention relates to an automatic transmission for a vehicle. It particularly relates to the automatic transmission comprising a toroidal-type continuously variable transmission including a torque converter, a forward-reverse switching mechanism, a impelling mechanism and a toroidal transmission unit which are sequentially provided from the driving source (engine) end of a vehicle, and further comprising a speed change control device for controlling speed change ratio and forward-reverse switching.
A toroidal type continuously variable transmission as an automatic transmission for a vehicle is described in JP-A-2-163562. This toroidal type continuously variable transmission has two toroidal transmission units in tandem, and is provided with a forward-reverse switching mechanism disposed on the preceding stage side of the toroidal transmission units.
In order to control the speed change ratio of the toroidal type continuously variable transmission, the above speed change control device obtains the ratio of the input rotational speed of the transmission as detected by a rotating speed sensor, to the output rotational speed, and changes the tilting angle of a power roller of the toroidal transmission unit according to the engine load, the vehicle speed and so on when the automobile is in motion to change the ratio of the output rotation to the input rotation, that is, the speed change ratio.
In such circumstances, the sensor for the input rotational speed of the transmission detects the output rotational speed of the torque converter. Accordingly, there is a difference between the transmission input rotational speed which the sensor inputs into the speed change control device for speed change control and the actual input rotational speed of the toroidal transmission unit.
However, the sensor for detecting the input rotational speed sometimes can not accurately detect said speed of the transmission under certain conditions.
When a driver switches the operating lever of the continuously variable transmission, from a drive range (D range) to a neutral range (N range) that is to say, puts the automobile in neutral during running, the forward-reverse switching mechanism becomes free in the N range, so that the rotation is not transmitted from the output shaft of the torque converter to the input shaft of the toroidal transmission unit. Accordingly, though the rotation of the output shaft of the torque converter corresponds to the engine rotational speed, the input shaft rotational speed of the toroidal transmission unit depends on the rotation of the output shaft at that time. Therefore it corresponds to the rotational speed corresponding to the vehicle speed and the speed change ratio.
In such cercumstances, the sensor for the input rotational speed of the transmission detects the output rotational speed of the torque converter. Accordingly, there is a difference between the transmission input rotational speed which the sensor inputs into the speed change control device for speed change control and the actual input rotational speed of the toroidal transmission unit.
When the driver switches the select lever again from N range back to D range ie. puts the automobile back into drive, in such a running condition that an input rotational speed difference results, the speed change control device determines the speed change ratio according to the input rotational speed when in the N range, which is different from the actual input shaft rotational speed of the toroidal transmission unit immediately after the above switching.
Therefore the transmission applies a speed change ratio determined according to rotational speed data different from the actual input rotational speed. Therefore the toroidal transmission unit is forced to conduct a sudden speed change operation, which results in the disadvantage that a comparatively large speed change shock is produced.
A methods for overcoming this disadvantage, is to dispose the forward-reverse switching mechanism not on the preceding stage side (input side) of the toroidal transmission unit, but to the subsequent stage side in order to connect the output side of the torque converter and the input side of the toroidal transmission unit to each other. As a result, the input rotational speed detected by the sensor always corresponds to the input shaft rotational speed of the toroidal transmission unit.
However, as the arrangement of the forward-reverse switching mechanism is changed in such a way, during normal running, the large torque rotation decelerated by the toroidal transmission unit is always applied to the forward clutch in the forward-reverse switching mechanism and reverse brake. These members need to have high durability, which results in the disadvantage that it is necessary to increase their capacity and the size.
It is, accordingly, an object of the present invention to prevent a speed change shock by always accurately detecting the actual input shaft rotational speed of the toroidal transmission unit and conducting speed change control according to this accurate detected rotational speed.
It is another object of the present invention to accurately detect the input rotational speed of the toroidal transmission unit without changing the arrangement of the forward-reverse switching mechanism to the subsequent stage side of the toroidal transmission unit.
In order to achieve the foregoing objects, the automatic transmission for a vehicle of the present invention comprises a toroidal type continuously variable transmission including a forward-reverse switching mechanism, an impelling mechanism and a toroidal transmission unit which are sequentially provided from the driving source end of the vehicle, and a speed change control device for controlling the operation of the transmission. A rotational speed signalling section is provided on one of the rotating members, which are connected to each other in the area from the output member of the forward-reverse switching mechanism to the input disc of the toroidal transmission unit, regardless of presence or absence of rotation transmission in the forward-reverse switching mechanism, an input rotational speed detecting part fitted to the transmission case side is positioned in the vicinity of the outer periphery of said rotational speed signalling section, and the input rotational speed detecting part detects the rotational speed of the rotating member provided with the rotational speed signalling section to be input to the speed change control device.
In the toroidal type continuously variable transmission for a vehicle of the present invention, even in the case where a driver switches the select lever of the automatic transmission from D range to N range during the running of a vehicle and the rotation is not transmitted to the forward-reverse switching mechanism, the rotational speed of one of the rotating members in the area from the output member of the forward-reverse switching mechanism to the input disc of the toroidal transmission unit, that is, the rotational speed which agrees with the input shaft rotational speed of the toroidal transmission unit is detected by the input rotational speed detecting part to be input to the speed change control device. Therefore the actual rotational speed input to the toroidal transmission unit, which is always detected accurately, continues to be input to the speed change control device while driving in the N range.
Accordingly, even if the driver switches the select lever of the automatic transmission from N range back to D range, the speed change control device controls the forward-reverse switching mechanism to transmit the rotation, controls the speed change ratio of the toroidal transmission unit on the basis of the actual input rotational rotating speed of the toroidal transmission unit while in the N range. Therefore the toroidal transmission unit is kept from performing sudden speed change operation and no speed change shock results.
In the present invention, the rotating member provided with the rotational speed signalling section is a loading cam in the impelling mechanism, and the rotational speed signalling sector may be provided on the outer peripheral part of the loading cam. The loading cam of the impelling mechanism, to which the output rotation of the forward and reverse switching mechanism is input, transmits the rotation to the input disc of the toroidal transmission unit through a cam roller and rotates substantially in unison with the input disc. Therefore the outer peripheral part of the loading cam expresses the maximum peripheral speed of the loading cam. The pitch of the signal section can be made smaller, so that the actual input rotational speed of the toroidal transmission unit can be detected accurately.
Further, in the present invention, the rotating member provided with the rotational speed signalling section may be a cam roller holder in the impelling mechanism, and the rotational speed detecting part may be provided on the outer peripheral part of the cam roller holder. The cam roller holder of the impelling mechanism is also rotated substantially in unison with the cam roller. Subsequently, the input disc also rotates when the loading cam transmits the output rotation of the forward-reverse switching mechanism through the cam roller to the input disc of the toroidal transmission unit, so that the actual input rotational speed of the toroidal transmission unit can be detected accurately.
Further, in the present invention, when the rotational speed detecting part is provided on the outer peripheral part of the cam roller holder, the loading cam of the impelling mechanism may have a smaller diameter than the cam roller holder of the impelling mechanism, and an outer peripheral part provided with the rotational speed signalling section of the cam roller holder may be formed in such a manner as to be extended in the axial direction, surrounding the outer peripheral part of the loading cam. The cam roller holder moves a little in the axial direction of the cam roller when the loading cam presses on the input disc through the cam roller with a force corresponding to transmission torque moving the input disc toward the output disc. Therefore if the outer peripheral part provided with the rotational speed signalling section of the cam roller holder is formed in such a manner as to be extended in the axial direction as described above, even if the cam roller holder moves in the axial direction, the input rotational speed detecting part can always detect the rotational speed of the rotational speed signalling section of the cam roller holder accurately. If the outer peripheral part of the cam roller holder is extended in the axial direction, as described above, and the loading cam is formed in such a manner as to have a smaller diameter than the cam roller holder and the outer peripheral part of the loading cam is surrounded with the outer peripheral part of the cam roller holder, the outer peripheral part of the cam roller holder can be extended in the axial direction without any increase in the radial dimension of the cam roller holder so as to eliminate the need of increasing the radial dimension of the toroidal type continuously variable transmission.
Further, in the present invention, the cam roller holder may have a smaller diameter than the input disc of the toroidal transmission unit. In such a configuration, the radial dimension of the cam roller holder will not be larger than the radial dimension of the input disc so as to eliminate the need of increasing the radial dimension of the toroidal type continuously variable transmission.
Further, in the present invention, a rotating member provided with the rotational speed signalling section may be an input disc of the toroidal transmission unit. The rotational speed signalling section may be provided on the outer peripheral part of the input disc, and the rotating member provided with the rotational speed signalling section may be also the output member of the forward-reverse switching mechanism. For detecting the actual input rotational speed of the toroidal transmission unit, it is desirable to detect the rotational speed of the input disc, so that if there is spatial room in the periphery of the input disc, and strengthening margins are provided in the input disc, the rotational speed signalling section may be provided on the outer peripheral part of the input disc.
Further, as an output member such as a pinion carrier or the like is the forward-reverse switching mechanism is always rotated substantially in unison with the input disc, the rotational speed signalling section may be provided on the output member.